1. Field of the Invention
The present invention generally relates to receiver circuits, and more specifically to a direct conversion satellite tuner that is integrated on a single semiconductor substrate.
2. Background Art
Direct satellite television broadcasts television signals directly from a satellite to a user, without any terrestrial re-transmission of the television signals. At the user location, a satellite dish receives the satellite signals, and a satellite receiver retrieves the baseband information for display on a standard television set.
In addition to television service, direct satellite television systems are also being configured to offer Internet service, including broadband or high speed Internet service.
Direct satellite television signals occupy a frequency spectrum from 950 MHz to 2150 MHz, with a channel spacing of approximately 29.16 MHz and a channel bandwidth of approximately 26.4 MHz. Therefore, approximately 40 channels are available in the 950–2150 MHz frequency band.
The modulation scheme that is utilized for satellite television signals is quadrature phase shift keying (QPSK). QPSK provides a data constellation having 4 possible positions, where each position represents two data bits. As a result, more than 40 information channels can be transmitted over the allotted frequency bandwidth since each constellation position represents two data bits. Future satellite television systems may be expanded to 8 PSK, further increasing the number of information channels that can be transmitted over the allotted frequency bandwidth.
Conventional satellite receivers utilize a hybrid configuration of multiple chips, boards, and/or substrates. For example, the local oscillator source, one or more mixers, and the baseband filter are typically on different substrates from each other. As a result, these multiple substrates must be assembled and electrically connected together, which increases manufacturing time and cost. Furthermore, electrical parasitics are associated with driving high frequency signals from one substrate to another, and can reduce electrical performance. Often times, individual components need to be tuned to compensate for the parasitics associated with driving a high frequency signal from one substrate to another.
Therefore, a single chip solution is highly desirable for satellite television tuners. The single chip solution will eliminate the need to connect multiple substrates together during manufacturing, and therefore will lead to a reduction in manufacturing time and cost. The single chip solution will likely improve electrical performance of the tuner as the parasitics associated with driving a signal off-chip will be eliminated. Additionally, the single chip solution will reduce the size of the satellite tuners, which becomes more critical for non-TV set applications. Therefore, what is required is a satellite tuner architecture that can be implemented on a single semiconductor substrate.
Additionally, the channel bandwidth requirements at baseband vary from one service provider to another, often based on geographic location. For example, a European service provider will typically have a different bandwidth requirement than a North American service provider. Conventional tuners do not have the ability to tune baseband bandwidth on chip in realtime. Therefore, the service provider must be identified during manufacturing so that the baseband filter bandwidth can set accordingly. Therefore, it would be advantageous for a single-chip tuner to have the capability of tuning the bandwidth of the baseband output so that the tuner could be mass produced without prior knowledge of the service provider and the corresponding baseband bandwidth requirement.